Most of this is wrong or slightly off.As a shooter I don't see it all as simple as that. Guns can kill. One type of shooting I have shot long ago in a competition is limited time with a target that is only shown for a limited time as well. 10 shots. Single shot gun so load aim fire. The target comes and goes. Maybe 1 used for aiming 2nd to fire. It doesn't take all that many seconds between shots. This to hit the centre of a playing card from 25yds.
Changes in this area mean that it will take a bit longer for each kill. The most effective change really is a ban on handguns. The USA have I believe banned SLR's - self loading rifles. The next bullet loads itself. Without this the the bolt has to be pulled back and pushed forwards to load the next bullet. Take the magazine away and the bolt has to be pulled back which ejects the cartridge case , next bullet pushed in and the bolt pushed forwards again.
A report just said that the USA has an average of 10 mass shooting a week. 200 so far this year. Seems this one used a hand gun but may have had a rifle. Also it seems Texas's gun laws are weaker than some other states. Mass may mean more than one person. No details. Hand guns were highlighted. They showed some one target shooting with an automatic pistol, self loading in other words. Variation of that sort of target shooting used to happen in the UK. It can't any more as they are banned even revolvers. I have shot a small automatic pistol when they were legal. The magazine could be emptied in under 10sec with careful trigger timing. Too expensive ammunition wise for me. Walmart discount the most popular killer bullet in the USA. In the movies we see people with hand guns and pockets full of magazines. Could that attract the wrong sort of person? It's easy to see why that sort of gun could prove popular even if the person owning them is ok.
Semi automatic weapons are still legal in most of the US. There was a ban for 10 years on Fully Automatic weapons, but it expired. Some states limit them, some don't. Even then there's bump stocks and conversions.
With bolt action weapons you can shoot rapidly and accurately with training. See the mad minute for more details. Or Lee Harvey Oswald.
Almost all handguns these days are semi automatic, the only real exceptions are hardcore target pistols.
In the US a mass shooting is at least 3 or 4 victims.